Is it correct? Possibly. "Must-see" is both a noun - as in "This is a must-see" - and an adjective - as in "This is a must-see event". The only time you could use a 'to' in this phrase is if you said "It's a must to see this event". In this case, the noun is 'a must', and the 'to' is part of the infinitive 'to see'.

I think, "A must see" is used in noun role: "This movie is a_must_see". "Must see" is another way of saying the same: "You must and see this movie", or "You must see this move".

Both are correct! This movie is a must see. or you can also say " You must see this movie , it's a great movie.

I think that a must see.